Fluorescent lamps have become extremely popular and well known within a variety of lighting systems. The popularity is due in large part to the excellent qualities of light produced together with the reduced amount of undesired heat production when compared with other systems such as incandescent lamps. In addition, the greater length of the elongated light producing tubes of fluorescent lamps provides extended large area lighting capabilities not enjoyed by competing lamp systems. A typical fluorescent lamp includes an elongated usually frosted glass tube formed in a straight line or curved shape. The glass tube is filled with a fluorescing gas and electrodes are positioned at each end of the glass tube. The fluorescent lamp produces light when energized by a suitable power source using the well known gas discharge phenomenon.
High-intensity discharge (HID) lamps are also well known an popular. They include mercury, metal halide, and high-pressure sodium lamps. A mercury lamp is an electric discharge lamp in which the major portion of the illumination is generated by the excitation of mercury atoms. A metal halide lamp is an electric discharge lamp in which the light is produced by radiation from an excited mixture of metallic vapor, i.e. mercury, and the products of the disassociation of halides, i.e. those of pallium, indium, sodium. A high-pressure sodium lamp is an electric discharge lamp in which the radiation is produced by the excitation of sodium vapor in which the partial pressure of the vapor during operation is of the order of 10.sup.4 N/m.sup.2.
Mercury lamps consist of a cylindrical transparent or translucent arc tube which confines the electric discharge and the associated gases. The tube is enclosed in a glass bulb or outer jacket to exclude air to prevent oxidation of the metal part and to stabilize operating temperatures and significantly reduce ultraviolet radiation emitted by the excitation of the vapors. The basic construction elements of a mercury lamp are the arc tube, which is fabricated from fused silica and filled with a drop of mercury, and a rare gas at low pressure; the electrodes; and the outer envelope, which may or may not utilize a phosphate coating formed upon the interior thereof to provide improved color rendering.
Metal halide lamps are very similar in construction to mercury lamps. The major difference is the addition of a metal halide within the arc tube. The outer bulb may optionally have an inner phosphate coating.
The basic components of a typical high-pressure sodium lamp are an arc tube of transparent polycrystaline or single-crystal alumina. The arc tube is filled with sodium, mercury, and a rare gas, i.e. xenon; electrodes; and an outer bulb silica glass envelope.
Mercury lamps provide moderate efficacy, very long life and lumen maintenance. Mercury lamps typically take approximately 3-5 minutes to start and ballasts are required.
Metal halide lamps provide high efficacy and good color rendering. They provide medium operating light spans and good optical control. Metal halide lamps are typically dimmable to about sixty percent (60%). They utilize ballasts.
High-pressure sodium lamps provide very high efficacy and long lamp life. Lumen maintenance is excellent, however, poor color rendering is typical. High-pressure sodium lamps are dimmable to approximately fifty to sixty percent (50-60%). They utilize ballasts.
One of the more interesting characteristics of fluorescent and HID lamps is their ability to operate at substantially reduced power levels once the gas discharge has been initiated during starting. Thus, typical fluorescent and HID lamps require a higher power level to initiate the light producing gas discharge effect but thereafter may be operated at substantially reduced voltages. In attempts to provide energy savings, particularly in fluorescent lamp systems, practitioners in the art have utilized this effect to provide a variety of energy conserving systems which facilitate reduced power operation once the gas discharge action has been initiated or "started."
For example, U.S. Pat. No. 4,513,224 issued to Thomas sets forth a FLUORESCENT-LIGHTING-SYSTEM VOLTAGE CONTROLLER having a three phase transformer which includes three auto-transformer windings each used for developing two reduced voltages. Three contactors selectively couple the full voltage and reduced voltages to the lighting systems. The contactors are switched in closed transition fashion to avoid power interruptions. An additional contactor is used for opening the winding neutral connections during the switching operation.
U.S. Pat. No. 4,766,352 issued to Widmayer sets forth a METHOD AND APPARATUS FOR STARTING AND OPERATING FLUORESCENT LAMP AND AUXILIARY BALLAST SYSTEMS AT REDUCED POWER LEVELS in which a capacitor is selected to provide effective starting of rapid start, preheat, and instant start type fluorescent lamps. A standard AC operated ballast transformer is operated at reduced power levels to achieve energy conservation. The capacitor is connected in series with the ballast primary winding and is selected to have a value producing ferro-resonance within the ballast transformer primary circuit.
U.S. Pat. No. 4,527,099 issued to Capewell, et al. sets forth a CONTROL CIRCUIT FOR GAS DISCHARGE LAMPS which includes anti-parallel connected controlled rectifiers connected in series with an AC source and the ballast and anti-parallel connected control rectifiers. A current limiting and energy diversion capacitor is series connected with the rectifiers and in shunt with the ballast. The controlled rectifiers of the series and shunt switching assemblies are controlled such that in any given half wave, the related controlled rectifier of the shunt switching means turn on to discharge a capacitor into the normally conducting controlled rectifier of the series switching means to produce a notch in the voltage waveform applied to the inductive ballast.
U.S. Pat. No. 4,464,606 issued to Kane sets forth a PULSE WIDTH MODULATED DIMMING ARRANGEMENT FOR FLUORESCENT LAMPS which includes a base driven high frequency push-pull transistorized inverter circuit used for energizing the lamps. The inverter is pulse width modulated to effect dimming. Transitory circuitry is provided for insuring rapid turn on and off of the inverter transistors. A photoresponsive sensor responds to ambient light and illumination produced by the lamps to control the pulse width modulator accordingly.
U.S. Pat. No. 4,435,670 issued to Evans, et al. sets forth an ENERGY CONSERVING INSTANT START SERIES SEQUENCE FLUORESCENT LAMP SYSTEM WITH OVERCURRENT PROTECTION which includes a power reducing capacitor connected in series with one or both of the lamps in a two lamp system. A protective device is connected within the circuit of the first lamp such that the high current flow produced by failure of the second lamp to start activates the protective device and prevents the system from being damaged.
U.S. Pat. No. 4,434,388 issued to Carver, et al. sets forth an ELECTRICAL LIGHTING CONTROLLER which is connected between a power line and a bank of lamps or other electrical energy consuming devices. The output level applied to the lamps is controlled by a variable autotransformer having a drive motor which in turn is controlled by an amplifier comparator circuit.
U.S. Pat. No. 4,339,690 issued to Regan, et al. sets forth an ENERGY SAVING FLUORESCENT LIGHTING SYSTEM which includes a reactants modifying capacitor coupled in series with first and second fluorescent lamps. A filament switch is operative to conduct filament heating current during the starting of the first lamp. The filament switch is coupled between filaments at opposite ends of the first fluorescent lamp and triggers to a low impedance state in response to the lamp starting voltage.
U.S. Pat. No. 4,256,993 issued to Morton sets forth an ENERGY SAVING DEVICE FOR RAPID-START FLUORESCENT LAMP SYSTEM which is connected in a series with one lamp of a two lamp rapid start fluorescent light system. The device includes a normally closed relay within the electrode circuit of one of the lamps and a power reducing capacitor in shunt with one of the relays contacts. Upon turning on the system, a solid state time delay and relay coil energizing circuit is actuated which opens the relay contacts only after the lamps have been started placing the shunt capacitor in series with the operating lamps to reduce the nominal power consumption.
U.S. Pat. No. 4,135,115 issued to Abernethy, et al. sets forth a WATTAGE REDUCING DEVICE FOR FLUORESCENT FIXTURES comprising the combination of a step up transformer, a resistor and two capacitors of a step up transformer, a resistor and two capacitors all of which are mounted externally of the ballast. The desired is wired in series with the ballast and one of the lamps to allow normal ballast voltages to be delivered to the lamp circuit.
U.S. Pat. 4,859,914 issued to Summa sets forth a HIGH FREQUENCY ENERGY SAVING BALLAST which provides energizing signals characterized by frequencies in the range from about sixty hertz to thirty megahertz. An oscillator and transformer provide the energizing signals which are transformer coupled to the lamp circuits.
U.S. Pat. No. 4,870,340 issued to Kral sets forth a METHOD AND APPARATUS FOR REDUCING ENERGY CONSUMPTION which includes switching apparatus for switching the load voltage off at arbitrary positions in the sine wave of the AC power applied while simultaneously providing a commutating path for any inductive current.
U.S. Pat. No. 4,965,492 issued to Boldwyn sets forth a LIGHTING CONTROL SYSTEM AND MODULE which includes a microprocessor control utilized to operate the lighting system at reduced power level while maximizing efficiency. The microprocessor and control circuitry continuously monitors the power applied and maintains the desired power level to maintain the preestablished light level selected.
While the foregoing described prior art systems have in various ways achieved energy saving and in many instances improved lighting characteristics, they are often complex and expensive to install and maintain. Thus, there remains a continuing need in the art for evermore improved and reliable lighting control systems which provide energy savings to the consumer.